1. Field of the Invention
The present invention relates to a polyacetal resin composition with small environmental impact capable of maintaining mechanical properties inherent in polyacetal resin and stably providing a molded body having an excellent appearance.
2. Description of Patent Literature
Polyacetal resin has high mechanical strength and rigidity; excellent oil resistance, organic solvent resistance, and self-lubricating property; a good balance in a wide temperature range; and an easy processability. Thus, the material is widely used, as representative engineering plastics, in mechanism parts and sliding parts for precision equipment, home appliances, OA equipment, vehicles, industrial materials, general merchandise, and the like. With recent expansion in applied areas of polyacetal resin, higher performance has currently been demanded. In such a trend, trials have been performed to enhance designability of molded bodies formed of polyacetal resin, by improving appearance and providing metal glossiness.
For instance, a production method of a molded body formed from adhesive resistant resin is proposed, in which a surface of a base material is blasted, and a metal film is formed on the surface through vacuum vapor deposition (for example, Patent Literature 1). When coating is employed to enhance appearance, coating material is also improved. A metal pigment dispersion is proposed, for instance, which is formed from a metal pigment in flake form and a binder or binder solution, the metal pigment having an extremely low content of products generated in fatty acid reaction or decomposition (for example, Patent Literature 2). Further, a powder coating composition is proposed, which contains thermoset resin powder on which a flake pigment is bound to a surface (for example, Patent Literature 3).
In addition, resin containing a glossy pigment is molded so as to display metal glossiness for designability. For instance, a method is proposed in which an optically changeable metallic pigment and a colorant are included for a predetermined amount into thermoplastic resin (for example, Patent Literature 4). Alternatively, a method is proposed in which a glossy pigment to be added in resin is included, the glossy pigment having particular aluminum particles (for example, Patent Literature 5).
Further, polytrimethylene terephthalate resin is proposed having excellent appearance, light resistance, and rigidity, the resin being included in vehicle exterior parts formed from resin (for example, Patent Literature 6).    [Patent Literature 1] Japanese Patent Laid-open Publication No. 2007-191738    [Patent Literature 2] Japanese Patent Application Publication No. H8-510294    [Patent Literature 3] WO Publication No. 2002/094950    [Patent Literature 4] Japanese Patent Laid-open Publication No. 2001-261978    [Patent Literature 5] WO Publication No. 2004/026970    [Patent Literature 6] WO Publication No. 2003/022926
The coating methods described in Patent Literatures 1 to 3 achieve a good appearance; however, the methods are not efficient since they require an extremely large number of controlled processes. In addition, the methods are not necessarily satisfactory given an impact of solvents on an environment or human bodies. Further, when the methods described in Patent Literatures 4 and 5 are applied to polyacetal resin in the above described trials, there are cases where mechanical properties inherent in the resin are deteriorated or an improvement in appearance is insufficient, because of an impact of heat generation during melt-mixing or an active site of a metal surface. Further, it is described in Patent Literature 6 that polyacetal resin and a glass fiber are mixed; that aluminum powder is added to the mixture; and that the materials are melt-kneaded. The method, however, does not achieve a good appearance, thus not providing a satisfactory molded body. Furthermore, no improving method for obtaining a good appearance was mentioned.
For polyacetal resin molded bodies used as design parts including a mechanical portion or a sliding portion in particular, a polyacetal resin composition with small environmental impact is thus demanded capable of maintaining mechanical properties inherent in the resin and stably providing molded bodies having an excellent appearance.